With potential applications ranging from field-emission displays and molecular electronics to nanocomposites, carbon nanotubes (CNTs) offer remarkable prospect in the development of multi-functional material systems. Reinforcement of carbon nanotubes (CNT) into a polymer matrix can improve several properties including electrical, mechanical, thermal, thermo-mechanical, chemical and optical properties. Exceptionally high mechanical properties such as strength, modulus, and resilience of the carbon nanotubes have fascinated consideration for the development of super strong light weight structures. However, the actual use of nanotubes in composites for structural applications has been disappointing despite huge promise, because of issues such as interfacial strength, alignment and dispersion. Several researchers have covered different aspects of CNT reinforcement in various polymer matrix systems. It has been observed that the use of CNT only as reinforcement at times failed to attain the superior mechanical properties in the composites. The combination of carbon fiber with carbon nanotubes, the modification in reinforcement scale relative to carbon fibers provides opportunity to unite potential benefits of nanoscale reinforcement with well-established fibrous composites to form multiscale hybrid micro/nanocomposites. By changing the reinforcement scale, it may be possible to modify the physical and mechanical properties of the composites. Hence, different routes have been adopted, remarkably a combination of carbon fiber (CF) and CNT that involves dispersion of CNT into polymer matrix (viz epoxy) followed by impregnation in carbon fabric. Nevertheless, the above compositions had the constriction of reinforcing <1% CNT and further it raised the viscosity of the CNT-epoxy mixer so much that it was hard to impregnate the entire fabric.
Reference may be made to US patent application no. 2014/0356613 wherein proposed is a method for making a carbon nanotube studded carbon fiber tow and matrix prepreg. The inventor applied silicon containing material to a tow of carbon fibers for the growth of carbon nanotube by chemical vapor deposition. In this process, the carbon fiber was unwound from spool & fed over an idler roller where silicon containing material was applied on the surface of carbon fiber tow. Silicon-based coating on surfaces of the carbon fibers supports carbon nanotube growth. Hydrocarbon organometallic compound are used as carbon source and transition metal are used as catalyst. From the matrix bath, matrix material (epoxy) was applied on the carbon nanotube studded carbon fiber tow with the help of roller and taken up on the take-up reel. Then carbon nanotube studded tow was sandwiched between an upper and lower, pre-filmed-matrix filmed on discharge patron material. In this way, the sandwich is directed through nip rollers to heat and compress the matrix film(s) into the sandwiched carbon nanotube studded tow. In conclusion, this is moved up on a round and hollow center as the prepreg material. However, the drawbacks of this patent application are that applying the silicon containing material, growth of carbon nanotube on each tow and laminating the tow by matrix consumes a lot of time and increases the cost of the process.
Reference may be made to US2013/043033 which recites that the prepreg; composite laminated component can be prepared by dispersing nanoparticles (carbon nanotubes or carbon nanofibers or nanographite) in inorganic solvent. This solution was sprayed on the support or substrate and solvent was removed by evaporation. The impregnation of resin into nanoparticle based Non-woven fabric with or without substrate was done by three methods. In the first method, resin was mixed in solvent and infiltrated into NNFW by dip-prepragging. Second by infiltration of the resin film into NNFW by roller lamination and in the third method infiltration of dilute resin into NNFW was done by curtain coating and/or roller lamination. However, the above proposed method of preparation of composite material is very tedious having numerous steps and consumes a lot of time.
Generally, two basic techniques have been followed until now for making hybrid composites First technique includes the dispersion of carbon nanotubes in epoxy matrix and utilization of this CNT dispersed epoxy as a matrix for the development of carbon nanotube-carbon fiber epoxy hybrid composites. Second involves the growth of carbon nanotubes on carbon fiber and their utilization as hybrid reinforcement for the development of carbon nanotube carbon fiber epoxy hybrid composites. However, none of the prior art documents disclose the preparation of hybrid composites by sandwiching CNT paper between the carbon fiber fabric.
Reference may be made to Thostenson et al. Journal of Applied Physics. 2002, Carbon nanotube/carbon fiber hybrid multiscale composites, volume 91, number 9 which recites the growth of carbon nanotubes directly on carbon fibers using chemical vapor deposition (CVD) and states that the selective reinforcement by nanotubes at the fiber/matrix interface likely results in local stiffening of the polymer matrix near the fabric/matrix interface, thereby improving load transfer. However, in the cited article, the CNTs were grown on carbon fiber using CVD which is a very complex process. Further, only the mechanical properties of CNT grown individual fiber were measured.
Reference may be made to Wang Baichen et al. 2012, Journal of applied Polymer Science, Investigation on some matrix-dominated properties of hybrid multiscale composites based on carbon/carbon nanotube modified epoxy, published online 27 Jun. 2012; pages 990-996, which discloses that carbon fiber reinforced epoxy composites modified with carbon nanotubes were fabricated to evaluate the effects of CNTs on hybrid multiscale composites. The study mainly focused on characterization of the state of dispersion of CNTs, analysis of the impregnation of continuous fiber reinforcement with CNTs/epoxy dispersion and assessment of shear properties of the resulting hybrid composites. However, the cited study is related to the dispersion of CNTs in epoxy resin and their use as matrix for the development of hybrid composites which is entirely different than the preparation of hybrid composites by sandwiching CNT paper between the carbon fiber layers as done in the present invention. Further, this paper used carboxylic acid functionalized multiwalled CNTs. Functionalization of CNT is not cost effective and increase the cost of the product. In addition, in this paper the carbon fiber plain fabrics were just immersed into a solution consisting of epoxy/curing agent/CNTs, whereas in the instant invention, the MWCNT paper was prepared and sandwiched into carbon fiber fabric which is a novel technique.
Reference may be made to Fawad Inam et al. 2010, Journal of Nanomaterials, Multiscale hybrid micro-nanocomposites based on carbon nanotubes and carbon fibers. Volume 2010 (2010); Article ID 453420, 12 pages which recites amino modified double walled carbon nanotube/carbon fiber/epoxy hybrid micro-nanocomposite laminates prepared by a resin infusion technique. The addition of small amounts of CNTs to epoxy resins for the fabrication of multiscale carbon fiber composites resulted in maximum enhancement in flexural modulus. Although this document relates to the dispersion of CNTs in epoxy matrix followed by vacuum impregnation of carbon fiber fabric by this CNT disperse epoxy for the development of multiscale composites, there is no sandwiching of CNT papers in this process. It is simply the impregnation of carbon fiber fabric with CNT dispersed epoxy. Further, the authors of this cited paper used amine modified double walled CNTs. The processing of amine CNT is very complex.
Thus, in short it may be summarized that till date, the composites are prepared either by dispersing CNTs in epoxy resin and their use as matrix or by growing CNT on carbon fiber and their use as hybrid reinforcement for the development of hybrid composites. However, none of the prior arts disclose a process for making hybrid composites in which CNT papers are sandwiched in between the carbon fiber fabric layers alternatively.
A major problem associated with the carbon fiber laminate reinforced polymer composites is the delamination, which is due to the ply-by-ply nature of carbon fabric reinforced resin composites. Susceptibility to delamination along interlaminar planes is an intrinsic and severe problem in the 2D polymer composites. The delamination substantially reduces the load carrying capacity and durability of composites and has led to disastrous structural failure. Thus, there is a need to improve the interlaminar shear strength which will be very much helpful for further improvement in the mechanical properties of the carbon fiber based polymer composites.
Accordingly, keeping in view the drawbacks of the hitherto reported prior art, the inventors of the present invention realized that there exists a dire need to provide a process to fabricate light weight, high strength carbon fiber, carbon nanotubes reinforced hybrid composites that enables a higher CNT-CF loading in the reinforced hybrid composite and that involves reinforcing MWCNTs in the form of papers by sandwiching them between the carbon fiber fabric layer.